During and after World War Two, TN9 Hadleigh was a complex site of 5.25"(133 mm) and 4.5" (115 mm) gun emplacements, ancillary buildings and structures, and accommodation huts. All of the accommodation huts have been demolished and the appearance of the site has changed with the addition of a banked reservoir and heaped soil and grass over the gun positions. However, potentially much remains. On the surface there is the post-war Operations Room/Generator Block, rare in the county. The Gun Store is one of only two - the other is at TN10 Vange. The On-Site Magazine is similarly one of only two - the other is at ZE7 Lippitts Hill. Two of the 4.5" emplacements and their command post may remain beneath the soil, but of major importance as no emplacements of this gun calibre remain in Essex. It is probable that the 5.25" emplacements remain intact or semi-intact beneath the ground.

Year of construction

1940

Owner

Essex County Council

Protected status

Scheduled Monument

Accessibility

Good

The site includes the remains of a World War II Heavy Anti-aircraft gunsite, documented in wartime records as 'TN9 (Thames North) Hadleigh', which is sited on a ridge of high ground known as Sandpit Hill, located to the north of Benfleet Creek and Hadleigh Marsh along the Thames estuary.The monument is in eight areas of protection. The first includes the four 5.25 (133 mm) inch gun emplacements sited in a square formation and the remains of associated nissen huts. The emplacements mostly survive below ground, having been infilled with soil. The outer edge of the north easternmost emplacement's ammunition gallery is visible above ground level. Their design is known from aerial photographs, the earliest of which dates to 1946 and shows the circular gun platforms with their internal rectangular structures. The emplacements have three levels: the upper level has the ammunition gallery from where the crew loaded the gun; the spent cartridge trench forms the next level (this includes a tunnel to the outside down which the spent shell cases were disposed); the pit at the lowest level houses the power mechanism. The gunsite's ammunition supplies were stored in nine ammunition huts positioned in a row to the immediate north west of the emplacements. The bases of two of these huts survive and are included in the scheduling. The surviving concrete floor of the huts carries the impression of the corrugated sheeting originally used for the superstructure.The second area to the west of the 5.25 inch emplacements is a combined Operations Room/Generator Block. This structure is built of heavy concrete with steel-framed, shuttered windows and measures some 22m long and a maximum of 15m wide. It belongs to the post-war period when the 5.25 inch gunsite was upgraded as a response to the Cold War threat and replaced an earlier wartime building.The third area, which encloses the 4.5 inch (115 mm) gun emplacements and associated structures, lies some 500m to the south west of the larger guns. Aerial photographs taken in 1946 show four octagonal emplacements in a semi-circle facing east towards the direction of incoming enemy aircraft. Each has five ammunition recesses built into the internal faces of the surrounding walls and is flanked by an integral bomb-proof shelter for the gun crew. In the centre of the semi-circle are a number of buildings and structures, including the command post. Now partly infilled, the two most southerly emplacements have concrete enclosures still visible. The foundations of the other two emplacements and elements of the command post and on-site magazine will survive as buried features. The fourth designated area lies to the west of the 4.5 inch emplacements and associated structures and encloses a second on-site magazine. This is a flat roofed concrete structure, partly below ground level, measuring some 15m by 8m.Four more protected areas lie in between the two sets of emplacements and enclose four ancillary buildings: the first is the Gun Store, two are simple, one-roomed structures, and the fourth is a water tower. The Gun Store is constructed of concrete, with a heavy steel door and four steel-framed, heavily shuttered windows on the southern side.The accommodation area for the gun crews (a series of lightweight barracks formerly located in between the two sets of gun emplacements) are not included in the scheduling.War Office documents relating to the equipment and manning of gunsite TN9 Hadleigh indicate that the four 4.5 inch guns were operational from 1940, whilst the four 5.25 inch guns came into operation during the course of 1944, with the latter being maintained as a Cold War deterrent during the post-war period.All modern fence posts are excluded from the scheduling, although the ground beneath them is included.